Land based vehicles such as cars and trucks when driven on roads generate low frequency noise known as road noise. As the wheels are driven over the road surface, such road noise is at least in part structure borne. That is to say, it is transmitted through structure elements of the vehicle such as tires, wheels, hubs, chassis components, suspension components such as suspension control arms or wishbones, dampers, anti-roll or sway bars and the vehicle body and can be heard in the vehicle cabin.
Until recently, the main approach for lowering the level of road noise in the vehicle cabin was to employ specifically optimized shapes and materials of the respective structure elements which attenuate vibrations and provide dedicated absorbers. This approach, however, generally leads to undesired constraints on the design of the vehicle as well as additional mass of the vehicle which adds to the overall fuel consumption.
Recently, active road noise control has been successfully applied to a number of vehicles using a high number of reference sensors mounted on structure elements of the vehicle contributing to the main transfer paths for road noise. The reference sensor locations are generally obtained by comparing various locations on a vehicle and their degrees of freedom (DoFs) that relate to the structure design of road noise transmitting components such as axles. Extensive simulations are often performed to determine the relation between critical structural locations that are influencing the Noise Vibration and Harshness (NVH) tuning of the vehicle and the reference sensor locations for active road noise control (ARNC) systems. In the ideal case, the reference sensors are placed such that they provide largely decorrelated signals which are coherent with the interior noise in the cabin. The ARNC systems process these signals from the reference sensors by applying digital filters to determine a, generally multi-channel, acoustic signal output by the speakers of the vehicle's audio system to cancel the transmitted road noise in a predetermined quiet zone which is typically arranged near the head rests for the driver and the passengers.
However, placement of the reference sensors can be a challenging task since the road noise performance of the vehicle can vary according to its structural design. From the NVH point of view, vibrations which are highly coherent with the interior noise are related with the structural dynamics of the vehicle and its axle design. In particular, the suspension and subframe architecture influence specific DoF that relate to the structural sensitivity of the structure. Generally, signals from various reference sensors are at least partly correlated such that a reduction of the number of the reference sensors would be possible. The determination of the optimal number and location of the reference sensors on the vehicle structure has been the object of costly and time-consuming mathematical optimization algorithms. Also, Principal Component Analysis (PCA) that is applied on the cross-spectra density matrix of the reference signals has been used to decorrelate potentially correlated reference signals. The PCA is however too expensive to be performed in real time in ARNC systems implemented in present day vehicles.
The present disclosure provides a method and a system for the automatic determination of the optimal arrangement of reference sensors for ARNC which overcomes the above mentioned drawbacks. The described method is in particular highly efficient and computationally inexpensive and can be readily applied to various designs of vehicle structures. The present disclosure also provides an ARNC system using a plurality of reference sensors whose arrangement is determined using the disclosed method.